The principle is already known of providing electromechanical print units with additional devices which make possible an automatic feed and removal of printing medias. Such an additional device is for example the above-mentioned single sheet conveyer which can be placed on the print unit and contains one or a plurality of receptacles for printing medias in sheet form. Assigned to the receptacles are separating mechanisms in the form of friction rollers which can be actuated by electromagnetic clutches through suitable control signals transmitted from the print unit and can pull out single sheets from the respective receptacle and convey them to the print position. Then the respective single sheet, after the recording of the information in the print unit, is removed from the print position again and deposited in a storage bin.
The single sheet conveyer to be attached to the electromagnetic print unit as an accessory is provided with a drive assigned individually to it and a control unit for controlling the drive and is controlled from the electromechanical print unit, for example by request signals. This gives rise to a relatively high mechanical and also electrical expenditure for the single sheet conveyer, because of which its extensive adoption has not yet been fully achievable.
Another additional device to be attached to electromechanical print unit is the continuous form conveyer with which printing medias in strip form can be pulled through a print unit, which have a perforation on their lengthwise edges in which the toothed tracks of two conveying units engage, which are also designated as Leporello conveyers. These continuous form conveyers in their use on electromechanical print units up to now have been used exclusively in the conveying direction of the printing media behind the print position, since they draw the strip-form printing media through the print unit so that when it comes out of the continuous form conveyer it can be deposited in a storage bin with zig-zag folding.
A relatively large amount of power was required up to now for driving the continuous form conveyer, since by the conveying principle of drawing a printing media through a print unit, the continuous form conveyer must expend not only the force required for merely conveying the printing media but in addition must also expend tensile force which is necessary in order to compensate for frictional effects caused by the repeated deflection of the printing media in the print unit. One disadvantage particularly important in this connection up to now was the increased danger of tearing out the perforations of the printing media due to the relatively high tensile force acting on its edges.